Syria's deputy foreign minister has told Sky News that he does not know if the regime has chemical weapons.

Faisal Mekdad said: "We don't know if we have them or not.

"We have said at different times, on different occasions, that even if we have them, we will not use them against our people."

Mr Mekdad also dismissed reports that the regime was preparing for Syrian president Bashar al Assad's exile as "laughable".

He said: "I assure you 100% that President Assad will never ever leave his country Syria."

The senior minister was responding to a Sky News report on continuing fighting in parts of Damascus, where Sky's Foreign Affairs Editor has reported the Syrian army is keeping control of the centre as the Free Syrian Army remain in the suburbs.

The comments about chemical weapons came a day after UN leader Ban Ki-moon formally warned Mr Assad against using such weapons in the country's civil war.

Mr Ban said any use of chemical arms would have "huge consequences" for the Syrian leader, adding to stern warnings made by US President Barack Obama and other Western leaders in recent days.

In Brussels, US Secretary of State Hillary Clinton reiterated concerns, saying "an increasingly desperate Assad regime might turn to chemical weapons" or lose control of them to militant groups.

UN spokesman Martin Nesirky said a letter outlining the warning was handed to Syrian authorities on Tuesday.

"The fundamental responsibility of the Syrian government is to ensure the safety and security of any such stockpiles, and of course the use of any such weapons would be an outrageous crime," Mr Nesirky said.

On Wednesday warplanes pounded suburbs of Damascus as regime forces battled rebels who are inching closer to the capital, according to the Syrian Observatory for Human Rights.

It said at least 53 people had been killed on Wednesday, including 21 in and around the city.

Damascus has in recent days been the focus of clashes following a major operation launched last week by the President's forces to prevent rebels from advancing on the capital, analysts say.